Engine coolants for the cooling system of an automotive vehicle usually contain ethylene glycol and a small percentage of diethylene glycol. This fluid is diluted with water to provide a 50% or lower concentration of glycol depending on the desired freezing point for the coolant system. Most companies that manufacture and/or distribute ethylene glycol for coolant systems add corrosion inhibitors to the solution to prevent corrosion of the copper-brass traditionally used in the manufacture of vehicle radiators.
These inhibitors usually are a mixture of one or more inorganic salts, such as phosphates, borates, nitrates, nitrites, silicates or arsenates, and an organic compound, such as benzotriazole, tolyltriazole or mercaptobenzothiazole, to prevent copper corrosion. The solution is generally buffered to a pH of 8 to 10 to reduce iron corrosion and to neutralize any glycolic acid formed in the oxidation of ethylene glycol. Most companies recommend a maximum of one or two years' service for their antifreeze coolant, however, it has been found that the average car owner does not follow the owner's instruction manual to maintain -20.degree. F. protection for the coolant system and does not check the coolant to determine if it is rusty or dirty. Many owners only add water when the antifreeze is lost through leakage or hose breakage. This is more likely to occur in the southern part of the country than in northern areas.
In normal passenger car service, 25% of the cars require coolant system servicing after only one year; after two years this percentage rises to 50%. With normal copper-brass radiators, and even more so with aluminum systems, it is extremely important that the antifreeze or coolant mixture contain 50 to 55% of the correctly inhibited ethylene glycol. A reduction to a mixture of 33% ethylene glycol--67% water will increase metal corrosion significantly. This is especially important with higher temperature coolant systems which are becoming more common with the increased use of emission controls.
Also, with the increasing emphasis on gas mileage of the new automobiles, cars are being downsized and reduced in weight through the substitution of light-weight metals or plastics for iron and steel where practical. In the automotive coolant systems, aluminum radiators are being utilized instead of the conventional copper-brass radiators previously used. As above noted, an aluminum radiator is more susceptible to the corrosive action of a coolant or antifreeze that is low in the percentage of ethylene glycol and/or where an insufficient amount of corrosion inhibitor is present in the coolant. In such a system, additional corrosion inhibitor must be added or the aluminum will begin to corrode by pitting at a rapid rate. The present invention ameliorates this corrosion problem by providing for the automatic addition of a corrosion inhibitor under corrosive conditions for the coolant.